IntelAcademic DIY 03 Managing Threads

Intel Do-It-Yourself ChallengeManaging Threads

Cdric Andreolliwww.Intel-Software-Academic-Program.com

[email protected] Software

2013-02-08

Agenda

Agenda

Introduction

Threads in Java

Threaded Servo Controller

Conclusion

Introduction

Introduction

In our previous example, we used a sleep to guaranty that the motor had enough time to end up its move.Intel CPUs have several cores and can execute many threads.This course will show you how to use your Intel CPU in a better way.

Threads in Java

Threads in Java

Java has its own synchronization model that use the keyword synchronized and the methods:

wait() notify() notifyall()

Threads in Java

synchronizedThe keyword synchronized can be applied to a method.

...or to a statement.

Threads in Java

Thread safe executionParts of code in a synchronized section on the same object can only be executed on 1 thread.

Those 2 snippets of code use a synchronized on this.

Threads in Java

Sample without synchronized

Threads in Java

Sample without synchronizedHere, there is no synchronized, threads are executed in parallel without synchronization.Threads output are mixed up.

Threads in Java

What happens ?As there is no synchronized area in this code, each thread computed the sum at its own speed and print out the result when it's done.

Threads in Java

Sample with synchronized

Threads in Java

Sample with synchronizedThreads are still executed in parallel but the synchronized area guaranty that only one thread at a time can access this part of the code.

Threads in Java

What happens ?As there is a synchronized region in this code, both threads can't access at the same time.

Threads in Java

Other possible scenarioWe don't know which thread will be the first to be executed.

Threads in Java

The wait()/notify() methodsMust be called in a synchronized region. The thread executing the wait() will be suspended. The object that called wait() will be the only one able to wake it. Waking up the thread can be done by calling notify() or notifyAll():

notify(): wakes up one thread locked on the calling objectnotifyAll(): wakes up all the treads locked on the calling object


Picture of the equipmentWe just plug 2 servos on the Phidget Advanced Servo controller.


OnMotorStop event?If you remember the Hello World, we needed to insert long sleeps after each command sent to the controller.The main reason is that the commands are executed asynchronously and no event is fired at the end of the command....In other word, the library doesn't provide any event to indicate that the position has been changed.


Multi-threadingTo take advantage of the multi-core intel platform, each servo will have it's own thread.Each servo will also have a queue containing the list of command to process.The thread related to the servo will execute an infinite loop and will try to execute a command from the queue at each iteration.


Multi-threadingWe want to fire an event when the servo is no more moving.We want to be able to end up the thread attached to each servo.


Project architectureWe are going to use 3 classes:

Servo: That represents a single servo. This calss manages its own thread.ServoAction: Represent an action/command that will be executed by the servo.ServoStopListener: A listener that will be called when the servo is no moremoving.


Class diagram


Servo class attributesThe Servo class represents a physical servo. If you remember the Hello World, each physical servo is identified by its number (from 0 to 7).The Servo object must be able to execute commands, so it needs to own a reference on the Phidget card (remember that all the commands are launched from a AdvancedServoPhidget object).


Servo constructor and class definition


Servo extends ThreadThe simplest way to manage a thread with the class Servo is by extending Thread.Then, Servo will have a method named start() that will be used to launch the thread.We need to add some code in the run() method. This method is executed when the user calls start() on a Thread object.


The run() methodThe run method is in charge of retrieving commands in the command queue.If the command queue is empty, the thread must call wait().The thread can be awaken when new commands are added to the queue.


The run() method


The executeAction() methodThis method is in charge of: Executing a command available in the

queue Firing an event when the servo is no more

moving.


The executeAction() method


Synchronized methodsAll the manipulations of the actionQueue and the isRunning boolean must be done in synchronized region.


Calls from the mainThe main method creates the AdvancedServo and initializes all the servos.


Calls from the mainWe can register a ServoStopListener.

We can start the servos even if no command has been added.


Calls from the mainAdding a new command is easy.

The call to addAction add a ServoAction to the actionQueue and then wakes up the sleeping thread.The servo will start moving!

Conclusion

Conclusion

Managing threadsWe've seen how to manage threads in Java and how to use synchronized, wait and notify.The threaded version is easier to use. You don't have to evaluate the time needed by the command anymore.The new version use very few CPU.

Conclusion

Samples availableThe full samples are available on www.http://intel-software-academic-program.com. Feel free to reuse this code and to modify it for your own projects.

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IntelAcademic DIY 03 Managing Threads